Multi-Chip Module Rate Adjustment

ABSTRACT

A Multi-Chip-Module (MCM) includes an MCM substrate and at least a data producing IC (DPIC) and a data-consuming IC (DCIC), both mounted on the MCM substrate and connected to one another through a high-speed bus having a fixed data rate. The DPIC is configured to send data to the DCIC by alternating between (i) first time periods during which the DPIC sends over the bus both produced data and dummy data that together have the fixed data rate of the bus, and (ii) second time periods during which the DPIC sends over the bus only dummy data at the fixed data rate, wherein a rate of the produced date and durations of the first time periods and the second time periods, are preset.

FIELD OF THE INVENTION

The present invention relates generally to multi-chip modules (MCMs),and particularly to efficient communication between integrated circuitsof MCMs.

BACKGROUND OF THE INVENTION

Communication between Integrated Circuits (ICs) in an MCM is typicallydone at high hit rates over a multitude of short point-to-point wires(Ultra-Short-Reach, or USR). In “Parallel Ultra-Short Reach Die-to-DieLinks,” PhD Thesis, Graduate Department of Electrical and ComputerEngineering, University of Toronto, 2017, Behzad Dehlaghi Jadiddescribes the challenges and the techniques that are typically used inUSR communications.

SUMMARY OF THE INVENTION

An embodiment of the present invention that is described herein providesa Multi-Chip-Module (MCM) including an MCM substrate and at least a dataproducing IC (DPIC) and a data-consuming IC (DCIC), both mounted on theMCM substrate and connected to one another through a high-speed bushaving a fixed data rate. The DPIC is configured to send data to theDCIC by alternating between (i) first time periods during which the DPICsends over the bus both produced data and dummy data that together havethe fixed data rate of the bus, and (ii) second time periods duringwhich the DPIC sends over the bus only dummy data at the fixed datarate, wherein a rate of the produced date and durations of the firsttime periods and the second time periods, are preset.

In some embodiments, the rate of the produced data in the first timeperiods is responsive to a data consumption rate in the DCIC. In someembodiments, start and end times of the second time periods are presetresponsive to time intervals in which the DCIC does not consume data.

In some embodiments, the high-speed bus includes a plurality of lanes,and whenever sending data, the DPIC is configured to either (i) sendproduced data concurrently on a set of the lanes, or (ii) send dummydata concurrently on the set of the lanes, and the DCIC is configured tocorrect errors in the received data responsive to detecting, at a giventime, produced data on one of the lanes in the set and dummy data onanother of the lanes in the set.

There is additionally provided, in accordance with an embodiment of thepresent invention, a method for data transfer in a Multi-Chip-Module(MCM). The method includes, for a data producing IC (DPIC) and adata-consuming IC (DCIC) that are part of the MCM and are connected toone another through a high-speed bus having a fixed data rate, defining(i) first time periods during which the DPIC sends over the bus bothproduced data and dummy data that together have the fixed data rate ofthe bus, and (ii) second time periods during which the DPIC sends overthe bus only dummy data at the fixed data rate, wherein a rate of theproduced date, and durations of the first time periods and the secondtime periods, are preset. Data is sent from the DPIC to the DCIC byalternating between the first time periods and the second time periods.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that schematically illustrates aMulti-Chip-Module (MCM), in accordance with embodiments of the presentinvention;

FIG. 2 is a block diagram that schematically illustrates Rate-AdjustCircuitry (RAC), in accordance with embodiments of the presentinvention;

FIG. 3 is a flow chart that schematically illustrates a method for rateadjustment in a Data Producing IC (DPIC), in accordance with anembodiment of the present invention;

FIG. 4 is a block diagram that schematically illustratesbubble-insertion in multi-lane inter-chip communication, in accordancewith embodiments of the present invention; and

FIG. 5 is a timing diagram that schematically illustratesbubble-insertion in multi-lane inter-chip communication, in accordancewith embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS Overview

The term multi-chip module (MCM) usually refers to an electronicassembly comprising multiple integrated circuits (ICs) and/or discretecomponents that are integrated, typically on a common substrate.Communication between the ICs of an MCM is done over short distances andis sometimes referred to as Ultra-Short-Reach (USR) communication. Wewill sometimes refer to the USR also as high-speed bus.

In high-performance MCMs, such as those used in network elements,communication between the ICs of the MCM may be fast and often carriedout by dedicated Serializer/Deserializer (SERDES) circuits that arecoupled to PHY units and transfer data at high rates over dedicated USRpoint-to-point wires. We will refer hereinbelow to the IC that transmitsthe data as Data Producing IC (DPIC), and to the IC that receives thedata over the dedicated USR wires as Data Consuming IC (DCIC).

For simple, relatively low-cost implementation, the rate of the USRcommunication may be fixed. however, the MCM may use differentdata-consumption rates in different applications or in differentconfigurations. Consequently, the data-consumption rate may be, at times(or always), lower than the fixed rate of the USR connection, and,hence, rate matching may be needed.

Embodiments of the present invention that are disclosed herein provideapparatuses and methods for the adjustment of data rate over thehigh-speed bus. In some embodiments, a DPIC comprises a rate-adjustmentcircuitry (RAC), which adds dummy data to the produced data that theDPIC sends over the high-speed bus, so that the high-speed bus data ratewill remain unchanged (dummy data, figuratively referred to as “bubbles”below, is a plurality of redundant data symbols which the DCIC removesfrom the input data stream).

According to embodiments, the RAC comprises a pulse generator, which ispreset to generate pulses at a rate that corresponds to thedata-consuming rate of the DCIC. The RAC further stores, in aFirst-In-First-Out (FIFO) memory, data that the DPIC produces. The RACis further configured to receive from a downstream unit (such as anencoder) read-symbol signals, at a rate that corresponds to the fixedrate of the dedicated high-speed bus. According to embodiments,responsive to a read-symbol input, the RAC sends Data symbols from theFIFO if the number of unread symbols in the FIFO is larger than a presetthreshold; and sends bubbles otherwise.

In some embodiments, the DCIC may periodically enter a Data-Pause periodand stop consuming data that the DPIC sends. In an embodiment, the timesat which the DCIC enters and exits the Data-Pause period are known whenthe DCIC and the DPIC are configured; the RAC can then track theData-Pause periods and send bubbles downstream rather than produceddata.

Thus, according to embodiments of the present. invention that areprovided herein, relatively inexpensive fixed-rate USR communication maybe used, wherein an RAC unit in the DPIC sends data and bubbles atcombined rate that equals the USR fixed rate. The data rate equals thedata consumption rate at the DCIC. When the DCIC is in a Data-Pauseperiod, the RAC sends bubbles only.

System Description

FIG. 1 is block diagram that schematically illustrates aMulti-Chip-Module (MCM) 102 in accordance with embodiments of thepresent invention. The MCM comprises a first Integrated Circuit (IC-A)104, which sends data to a second integrated Circuit (IC-B) 106, over anUltra-Short-Range (USR) 108 connection.

In practice, the MCM may comprise other integrated circuits and/ordiscrete components, which are typically assembled on a commonsubstrate; such elements are not shown in FIG. 1, for clarity. Moreover,both IC-A 104 and IC-B 106 may be coupled to other ICs ;or to eachother) by additional connections that are not shown, USR or others, andtransfer data in any direction. Thus, FIG. 1 illustrates solely a datapath within MCM 102, wherein IC-A is a Data-Producing IC (DPIC) and IC-Bis a Data-Consuming IC (DCIC). In the description below we willsometimes refer to IC-A and IC-B as DPIC and DCIC, respectively.

The required rate of data transmission over the USR may vary accordingto the application, which may take place, for example, when theconfiguration of the MCM changes. In the example embodiment illustratedin FIG. 1, however, the rate is fixed, and equals at least the highestdata rate that may be required; hence, the DCIC should adjust the ratewhen sending data over the USR connection.

DPIC 104 comprises Rate-Adjust Circuitry (RAC) 110 which adjusts therate of data transmission by adding dummy data (also referred to as“bubbles” typically comprising null symbols) and sends data at the USRfixed transmission rate to an Encoder 112. The encoder encodes data intosymbols, and may perform functions such as scrambling, addingerror-correction bits, interleaving, 64/66 encoding, and/or any othersuitable function. Encoder 112 sends the encoded data to aTx-Seriallizer 114, which converts the symbols into high speed serialstreams, in one or more lanes, and sends the serial streams to a Tx-PHY116. The Tx-PHY typically modulates the input bit streams and sends themodulated streams over the physical wires of the USR connection, using,for example, 4-Level Pulse Amplitude Modulation (PAM4) (note that ifPAM4 is used, two of the bits of the encoded symbols are not convertedto serial by Tx-Seriallizer 114; rather, the two bits aredigital-to-analog converted by the PAM4). Due to the addition ofbubbles, the rate over USR connection 108 is fixed.

In DCIC 106, the inverse operations take place—an Rx-PHY 118 demodulatesthe input from USR 108 and sends bit streams to an Rx-DESER 120, whichconverts the bit-streams into encoded symbols. A Decoder 122 thendecodes the encoded symbols and forwards the decoded symbols to aBubble-Remover 124, which strips the bubbles from the stream, andforwards the original data that was input to RAC 110 for furtherprocessing at the DCIC.

In some embodiments, the DCIC alternates between periods in which theDCIC consumes data (“Data-Consumption Periods”) and periods in which theDCIC does not consume data (“Data-Pause periods”). RAC 110 of DPIC 104is configured to track such periods and send bubbles rather thatproduced data when the DCIC does not consume data. Accurate tracking ispossible because the DPIC and the DCIC share the same clock input andcan therefore track the same time events.

Thus, according to the example embodiment illustrated in FIG. 1 anddescribed above, a DPIC can transfer data at various preset rates over aUSR that sends data at a fixed rate. MCMs according to the exampleembodiment will comprise USRs that are optimized to a singletransmission frequency and may be less expensive.

As would be appreciated, the structures of MCM 102, DPIC 104 and DCIC106 described above are cited by way of example. MCMs, DPICs and DCICsin accordance with the disclosed techniques are not limited to thedescription hereinabove. In alternative embodiments, for example,encoder 112 may precede RAC 110; and/or Bubble Remover 124 may precedeDecoder 122. In some embodiments, respective to the modulation techniqueof Tx-PHY 116, the number of bits that are converted to analog by Tx-PHY116 rather than Tx-Seriallizer 114 may be less or more that 2; e.g., 0for NRZ. and 8 for QAM256.

FIG. 2 is a block diagram that schematically illustrates Rate-AdjustCircuitry (RAC) 110 used in DPIC 104, in accordance with embodiments ofthe present invention. The RAC receives produced data and sendsrate-adjusted data to Encoder 112 (see FIG. 1).

According to the example embodiment illustrated in FIG. 2, the RACcomprises an input First-In-First-Out (FIFO) 200, which is configured totemporarily store data produced by the DPIC. As would be appreciated,such FIFO may exist in upstream units of the DPIC (that are not shown),and thus may not be needed in the RAC. However, for the completeness ofthe description herein, the input FIFO (or an additional input FIFO) isimplemented in the RAC.

An Output FIFO 202 that is coupled to the data output of the input-FIFO,temporarily stores data read from the input-FIFO. The transfer of datafrom the input-FIFO to the output-FIFO is controlled by an AND gate 204,which send a Read signal to the input-FIFO and a Write signal to theoutput-FIFO (in practice, the read may precede the write by one or moreclock cycles).

A pulse generator 206 is configured to generate pulses at a preset ratewhich matches the rate of data consumption in the DCIC. In someembodiments, the configuration of the DCIC (and, hence, the dataconsumption rate) is signaled to the DPIC upon initialization, and,thus, the pulse generator rate may be preset to match the dataconsumption rate.

According to the example embodiment illustrated in FIG. 2, the DCIC mayalternate between a data-pause period of a first preset duration, and adata-consumption period of a second preset period. While in a data-pauseperiod, the DCIC does not consume data (for example, the DCIC may addspecial symbols to the received data). The DCIC may alternate between adata consumption first period and a data-pause second period (forexample, the first period may equal the time it makes to transmit 1638364/66 bit words, and the second period—the time it takes to transmit asingle 64/66 bit word). The durations of the first and second periodsmay be derived from the configuration of the DCIC and notified to theDPIC upon configuration or reset.

According to the example embodiment, a Period-Sequencer 208 tracks theData-Pause and Data-Consumption periods of the DCIC. Thus, AND gate 204,which is coupled to both Pulse-Generator 206 and Period-Sequencer 208,will initiate transfer of data from the Input-FIFO to the Output-FIFO atthe data consumption frequency, pausing when the DCIC is in theData-Pause period.

The RAC receives from a downstream unit (e.g. encoder 12, FIG. 1)Read-Symbol pulses at a rate that corresponds to the USR connectionrate. Responsive to the Read-Symbol signal, the RAC will output eitherdata or bubbles.

A FIFO-Depth-Comparator 210 compares the depth of the Output-FIFO (e.g.,the number of entries that are written but not yet read) to a presetthreshold TH. The threshold may be set, for example, responsive to thesize of the data units that the encoder processes in a clock cycle. AnAND gate 212 outputs a Read-Output-FIFO signal to Output-FIFO 202 if,when a Read-Symbol pulse is input, and the depth of the Output-FIFO islarger than the threshold.

The Read-Output-FIFO signal (or a delayed version thereof) also controlsa Multiplexor 214, which forwards downstream (e.g., to the encoder) datafrom the Output-FIFO or, if the Output-FIFO's depth is not greater thanthe threshold, bubble data.

Thus, according to the example embodiment illustrated in FIG. 2, the RACadds bubbles to the produced data, responsively to the data-consumptionrate and to the data-pause periods in the DCIC, and thus keeps the USRrate fixed.

As would be appreciated, the structure of RAC 10 described above iscited by way of example. RACs in accordance with the disclosedtechniques are not limited to the description hereinabove. For example,in some embodiments, Input-FIFO 200 may be (as described above)implemented in an upstream unit. In an embodiment, Output-FIFO 202,FIFO-Depth-Comparator 210 and AND gate 212 are not implemented; rather,Multiplexor 214, responsive to a Read-Symbol input, transfers data fromthe input FIFO if the Input-FIFO is not empty and transfers a bubbleotherwise. In some embodiments period sequencer 208 and Pulse-Generator206 are merged into a single timing-control unit.

FIG. 3 is a flow chart 300 that schematically illustrates a method forrate adjustment in a DPIC, in accordance with an embodiment of thepresent invention. The flowchart is executed by RAC 110 (FIG. 1).

The flow chart comprises a DATA-IN flow (right part of FIG. 3) and aDATA-OUT flow (left). The RAC executes both flows concurrently.

The Data-In flow starts at a Rate-and-Period-Setting step 302, whereinthe RAC sets the rate of pulse generator 206 and the periods ofPeriod-Sequencer 208 (both illustrated in FIG. 2). The RAC sets the rateof the pulse generator to match the data consumption rate in the DCICand sets the durations of the first and second periods of thePeriod-Sequencer to match the durations of the Data-Consumption andData-Pause periods, respectively. The duration of the two periods andthe data-consumption rate are preset; e.g., during configuration orduring reset.

Next, in an Initializing-Period-Sequencer step 304, the RAC initializesPeriod-Sequencer 208, so that the periods that the Period-Sequencergenerates will be synchronized to the corresponding periods of the DPIC.This can be done, for example, by sending a start signal from the DPICto the DCIC, or, for another example, if both the DPIC and the DCICshare the same reset signal (other synchronization methods may be used,as would be appreciated by those skilled in the art). The PJC nextenters a First Period-Check step 306 and checks if Periods-Sequencer 208is in the First Period. If the Periods Sequencer is in the first periodthe RAC will proceed to a Pulse-On-Check step 308, and check if thepulse that Pulse-Generator 206 (FIG. 2) generates is on.

If, in step 308, the pulse is on, the RAC will enter a Data-Transferstep 310, read the least recent entry of Input-FIFO 200 and write theentry into Output-FIFO 202 (both FIFOs illustrated in FIG. 2); and,then, reenter step 306.

If, in step 306, the period sequencer is in the second period or if, instep 308, the pulse is not on, The RAC will reenter step 306.

To sum-up, in the Data-In flow, the RAC, after setup and initialization,transfers data from the Input-FIFO to the Output-FIFO at a ratecorresponding to the DCIC data consumption rate, and stops transferringdata when the DCIC is in the data-pause period.

The Data-Out flow starts at a Data-Request-Check step 312, which the RACcontinuously executes until the RAC receives a Read-Symbol request froma downstream unit (e.g., from Encoder 112, FIG. 1), whereupon the RACenters a FIFO-Depth-Check step 314.

In step 314, the RAC checks if the depth of Output-FIFO 202 (FIG. 2)(i.e. the number of FIFO entries that have been written but have not yetbeen read) is greater that a preset threshold. The threshold may be set,for example, responsive to the size of the data units that the encoderprocesses in a clock cycle. If the Output-FIFO depth is greater than thethreshold, the RAC will enter an Output-FIFO-Read step 316, read theleast recent Output-FIFO entry, and then, in a Sending-Date step 318,send the read data downstream (e.g., to Encoder 112). If, in step 314,the depth of Output-FIFO 202 is not greater than the threshold, the RACwill enter a Sending-Bubble step 320 and send a bubble downstream. Afterboth steps 318 and 320 the RAC reenters step 312.

In summary, the RAC, when executing the Data-Out flow, responds to aRead-Symbol request by reading and sending a symbol from the output-FIFOif the Output-FIFO depth exceeds a threshold, and by sending a bubbleotherwise.

As would be appreciated, flow 300 described above is cited by way ofexample. Flows in accordance with the closed techniques are not limitedto the description hereinabove. For example, in alternative embodiments,some of the steps may be done at a different order (e.g., steps 306 and308 may be interchanged) , or executed concurrently. Data-In flow anddata-Out flow may be merged to a single flow or split to more parallelflows. The flow chart may be executed by hardware, by software or by acombination of hardware and software.

Mitigating USR Communication Noise Effects

USR communication, like any other communication system, is prone tonoise, characterized, for example, by a bit-error-rate measure (othermeasures are sometimes used in addition or instead of bit-error-rate). Avariety of error correction techniques may be employed in USRcommunication, reducing not eliminating) the bit-error rate.

For data symbols (as opposed to control symbols), the damage from asingle erroneous symbol that the DCIC receives is relatively small.However, if due to noise, a bubble is interpreted as a data symbol, orif a data symbol is interpreted as a bubble, all the following symbolsmay be misinterpreted (shifted), and the damage may be substantial.

In some embodiments according to the present invention, USRcommunication is done over multiple lanes; and the DPIC sends bubblesconcurrently on all lanes. The DCIC will then be able to substantiallydecrease the probability that bubbles will be missed, and thatnon-bubble symbols will be mistaken for bubbles. For example, if threelanes are used and the DPIC sends bubbles on all three lanes, the DCICmay be configured to consider all three symbols as bubbles even if onlytwo of the received symbols are bubbles, and, if a single bubble isreceived in one of the three lanes, to convert the bubble to anarbitrary non-bubble (albeit most probably wrong) symbol. Thus, theprobability to falsely interpret a bubble as a non-bubble or anon-bubble as a bubble will be significantly reduced.

In an embodiment, the probability that a data symbol will be transformedto a bubble symbol is negligible and, therefore, ignored. The DCIC,whenever a bubble is received in any lane, converts the concurrentsymbols on all other lanes to bubbles.

FIG. 4 is a block diagram. 400 that schematically illustratesbubble-insertion in a multi-lane inter-chip communication, in accordancewith embodiments of the present invention. AnInput-FIFO-Lane-Distributor 402 distributes to lanes and temporarilystores the produced data (three lanes in the example embodimentillustrated in FIG. 4). The output from Input-FIFO-Lane-Distributor 402is three parallel symbols, which are written to a 3-symbol-wideOutput-FIFO 404.

The control circuits of Input-FIFO-Lane-Distributor 402 an Output-FIFE)404 are similar, respectively, to the control circuits of Input-FIFO 200and Output-FIFO 202 (FIG. 2) (as would be evident, the rate of pulsegenerator 206 is adjusted to account for three lanes).

A Multiplexor 406 either outputs three parallel symbols from theOutput-FIFO or three bubbles, responsive to a control that is also usedfor reading data from the Output-FIFO. Multiplexor 406 is likeMultiplexor 214 (FIG. 2), except that Multiplexor 406 outputs threeparallel symbols—data or bubbles—for each read-symbol request.

Thus, according to the example embodiment illustrated in FIG. 4, highreliability is achieved while still using bubbles to maintain a fixed.USR transmission rate.

As would be appreciated, block diagram 400 described above is cited byway of example. Multi-lane bubble-insertion circuits in accordance withthe disclosed techniques are not limited to the description hereinabove.For example, in alternative embodiments, the number of lanes can be anyinteger number larger than 1, fixed or programable. In some embodiments,the distribution to lanes is done in later stages such as the encoder,and bubble replication for all lanes is merged with lane distribution.

FIG. 5 is a timing diagram 500 that schematically illustratesbubble-insertion in a multi-lane inter-chip communication, in accordancewith embodiments of the present invention. An Input-Data-Symbolswaveform 502 illustrates sequential produced-data symbols that RAC 10receives, sequentially numbered from 1 to 12. A Data-Symbols-in-Laneswaveform 504 illustrates the data symbols distributed to three lanes—theRAC forwards symbols 1,4 and 10 to a first lane; symbols 2,5,8 and 11 toa second lane; and, symbols 3,6,9 and 12 to a third lane.

As described above (with reference to FIG. 4), bubbles are inserted inail three lanes concurrently. A USR-Rate-Data-with-Symbols waveform 506illustrates the data that the RAC outputs at USR communication rate. Ascan be observed, the PAD adds bubbles in triplets, on all three lanes.

The configuration of MCM 102, RAC 110 and all subunits thereof, as wellas method 300 and waveform 500, are example configurations, methods andwaveforms that are shown pure y for the sake of conceptual clarity. Anyother suitable configurations, methods and waveforms can be used inalternative embodiments.

In various embodiments, DPIC 4 RAC 10 and DCIC 6 may be implementedusing suitable hardware, such as one or more Application-SpecificIntegrated Circuits (ASIC) or Field-Programmable Gate Arrays (FPaA), ora combination of ASIC and FPGA.

Although the embodiments described herein mainly address rate adjustmentin MCMs, the methods and systems described herein can also be used invarious other systems and applications.

It will be appreciated that the embodiments described above are cited byway of example, and that the present invention is not limited to whathas been particularly shown and described hereinabove. Rather, the scopeof the present invention includes both combinations and sub-combinationsof the various features described hereinabove, as well as variations andmodifications thereof which would occur to persons skilled in the artupon reading the foregoing description and which are not disclosed inthe prior art. Documents incorporated by reference in the present patentapplication are to be considered an integral part of the applicationexcept that to the extent any terms are defined in these incorporateddocuments in a manner that conflicts with the definitions madeexplicitly or implicitly in the present specification, only thedefinitions in the present specification should be considered.

1. A Multi-Chip-Module (MCM), comprising: an MCM substrate; and at leasta data producing IC (DPIC) and a data-consuming IC (DCIC), both mountedon the MCM substrate and connected to one another through a high-speedbus having a fixed data rate, wherein the DPIC is configured to senddata to the DCIC over the high-speed bus having the fixed data rate, byalternating between (i) first time periods during which the DPIC sendsover the bus both produced data and dummy data that together have thefixed data rate of the bus, and (ii) second time periods during whichthe DPIC sends over the bus only dummy data at the fixed data rate,wherein a rate of the produced data and durations of the first timeperiods and the second time periods, are preset.
 2. The MCM according toclaim 1, wherein the rate of the produced data in the first time periodsis responsive to a data consumption rate in the DCIC.
 3. The MCMaccording to claim 1, wherein start and end times of the second timeperiods are preset responsive to time intervals in which the DCIC doesnot consume data.
 4. The A Multi-Chip-Module (MCM), comprising: an MCMsubstrate; and at least a data producing IC (DPIC) and a data-consumingIC (DCIC), both mounted on the MCM substrate and connected to oneanother through a high-speed bus having a fixed data rate, wherein theDPIC is configured to send data to the DCIC by alternating between (i)first time periods during which the DPIC sends over the bus bothproduced data and dummy data that together have the fixed data rate ofthe bus, and (ii) second time periods during which the DPIC sends overthe bus only dummy data at the fixed data rate, wherein a rate of theproduced data and durations of the first time periods and the secondtime periods, are preset, and wherein the high-speed bus comprises aplurality of lanes, wherein, whenever sending data, the DPIC isconfigured to either (i) send produced data concurrently on a set of thelanes, or (ii) send dummy data concurrently on the set of the lanes, andwherein the DCIC is configured to correct errors in the received dataresponsive to detecting, at a given time, produced data on one of thelanes in the set and dummy data on another of the lanes in the set.
 5. Amethod for data transfer in a Multi-Chip-Module (MCM), the methodcomprising: for a data producing IC (DPIC) and a data-consuming IC(DCIC) that are part of the MCM and are connected to one another througha high-speed bus having a fixed data rate, defining (i) first timeperiods during which the DPIC sends over the bus both produced data anddummy data that together have the fixed data rate of the bus, and (ii)second time periods during which the DPIC sends over the bus only dummydata at the fixed data rate, wherein a rate of the produced data, anddurations of the first time periods and the second time periods, arepreset; and sending data from the DPIC to the DCIC over the high-speedbus having the fixed data rate by alternating between the first timeperiods and the second time periods.
 6. The method according to claim 5,wherein defining the first and second time periods comprises setting therate of the produced data in the first time periods responsively to adata consumption rate in the DCIC.
 7. The method according to claim 5,wherein defining the first and second time periods comprises presettingstart and end times of the second time periods responsively to timeintervals in which the DCIC does not consume data.
 8. The methodaccording to claim 5, wherein the high-speed bus comprises a pluralityof lanes, wherein sending the data comprises sending from the DPICeither (i) produced data concurrently on a set of the lanes, or (ii)dummy data concurrently on the set of the lanes, and comprising, in theDCIC, correcting errors in the received data responsive to detecting, ata given time, produced data on one of the lanes in the set and dummydata on another of the lanes in the set.
 9. The MCM according to claim4, wherein the rate of the produced data in the first time periods isresponsive to a data consumption rate in the DCIC.
 10. The MCM accordingto claim 4, wherein start and end times of the second time periods arepreset responsive to time intervals in which the DCIC does not consumedata.
 11. The MCM according to claim 1, wherein the rate of the produceddata is always lower than the fixed data rate of the high-speed bus. 12.The MCM according to claim 1, wherein the DPIC comprises an inputFirst-In-First-Out (FIFO) memory in which it stores the produced data tobe transmitted to the DCIC and is configured in the first time periodsto send data symbols when a number of unread symbols in the FIFO memoryis larger than a preset threshold and to send dummy data otherwise. 13.The MCM according to claim 1, wherein the second time periods are timesat which the DCIC stops consuming data from the DPIC and the first timeperiods are times at which the DCIC consumes data from the DPIC.